Wind power is considered one of the cleanest, most environmentally friendly energy sources presently available, and wind turbines have gained increased attention in this regard. A modern wind turbine typically includes a tower, a generator, a gearbox, a nacelle, and a rotor having a rotatable hub with one or more rotor blades. The rotor blades capture kinetic energy of wind using known airfoil principles. The rotor blades transmit the kinetic energy in the form of rotational energy so as to turn a shaft coupling the rotor blades to a gearbox, or if a gearbox is not used, directly to the generator. The generator then converts the mechanical energy to electrical energy that may be deployed to a utility grid.
Each rotor blade extends from the hub at a root of the blade and continues to a tip. A cross-section of the blade is defined as an airfoil. The shape of an airfoil may be defined in relationship to a chord line. The chord line is a measure or line connecting the leading edge of the airfoil with the trailing edge of the airfoil. The shape may be defined in the form of X and Y coordinates from the chord line. The X and Y coordinates generally are dimensionless. Likewise, the thickness of an airfoil refers to the distance between the upper surface and the lower surface of the airfoil and is expressed as a fraction of the chord length.
The inboard region, i.e., the area closest to the hub, generally requires the use of relatively thick foils (30%≤t/c≤40%). The aerodynamic performance of conventional airfoil designs, however, degrades rapidly for thicknesses greater than 30% of chord largely due to flow separation concerns. For thicknesses above 40% of chord, massive flow separation may be unavoidable such that the region of the blade may be aerodynamically compromised.
In some instances, flatback airfoils may be used in the inboard region to allow for higher lift of thick airfoils but at reduced chords. Traditional flatback designs, however, can be extremely costly and complicated to manufacture.
Roundback airfoils are substantially less expensive and less complicated to manufacture than flatback airfoils. Although roundback airfoils allow the airflow to “feel” a larger trailing edge thickness (and hence the potential for increased lift performance), such airfoils can create flow separation on the curved surface that is sensitive to small details in the inflow. As such, the separation location and hence the lift from the roundback airfoil can fluctuate to an unacceptable extent.
Thus, there is a need for a new and improved airfoil configuration for a wind turbine rotor blade that addresses the aforementioned issues. More specifically, an airfoil that provides improved aerodynamic performance particularly with respect to the inboard region would be advantageous.